1. Field of the Invention
The present invention relates to a drive system that has a DC drive device, which is driven by DC power, and an AC drive device, which is driven by AC power, and is given AC power. For example, the invention relates to a liquid crystal display apparatus.
2. Description of the Related Art
FIG. 21 is a sectional view showing a conventional liquid crystal display apparatus 1. The liquid crystal display apparatus 1 performs image display by transmitting backlight 17 to a liquid crystal display substrate 16 selectively. The liquid crystal display apparatus 1 includes a housing 19, discharge tubes 5 that emit the backlight 17, and an electric circuit group 18 for supplying power to the discharge tube 5.
FIG. 22 is a block diagram showing the conventional liquid crystal display apparatus 1. The liquid crystal display apparatus 1 is connected to a commercial power supply 2 and is driven by AC power given from the commercial power supply 2. The liquid crystal display apparatus 1 has a DC conversion device 3, an inverter device 4, the discharge tubes 5, an image processing circuit 6, a liquid crystal driver 7, and a speaker 8.
The DC conversion device 3 converts commercial AC power given from the commercial power supply into DC power. The DC conversion device 3 gives the converted DC power to the inverter device 4, the image processing circuit 6, the liquid crystal driver 7, and the speaker 8. The inverter device 4 converts the DC power given from the DC conversion device 3 into AC power having a frequency and a voltage capable of driving the discharge tubes 5. Then, the inverter device 4 gives the converted AC power to the discharge tubes 5. In addition, the image processing circuit 6, the liquid crystal driver 7, and the speaker 8 are driven by the DC power given from the DC conversion device 3.
FIG. 23 is a block diagram showing the conventional DC conversion device 3 and the conventional inverter device 4. The DC conversion device 3 has a first DC power generating circuit 10, a first alternating power generating circuit 11, a first transforming circuit 12, and a second DC power generating circuit 13. The DC conversion device 3 converts commercial AC power into DC power with the first DC power generating circuit 10. The DC conversion device 3 converts the converted DC power into high-frequency AC power with the first alternating power generating circuit 11. Then, the DC conversion device 3 transforms the high-frequency AC power into AC power of a target voltage with the first transforming circuit 12 and converts the transformed AC power into DC power with the second DC power generating circuit 13. In this way, the DC conversion device 3 generates DC power of a target voltage and gives the generated DC power to the inverter device 4, the image processing circuit 6, the liquid crystal driver 7, and the speaker 8.
The inverter device 4 has a second alternating power generating circuit 14 and a second transforming circuit 15. The inverter device 4 converts DC power given from the second DC power generating circuit 13 into AC power having a target frequency with the second alternating power generating circuit 14. Then, the inverter device 4 converts the AC power into AC power having a target voltage with the second transforming circuit 15. Consequently, the inverter device 4 generates AC power having a voltage and a frequency capable of driving the discharge tubes and gives the generated AC power to the discharge tubes 5. The discharge tubes 5 are driven to emit light as the AC power is given from the inverter device 4. Such a conventional inverter device 4 is disclosed in Japanese Unexamined Patent Publications JP-A 6-197555 (1994), JP-A 2000-12256, and JP-A 56-88678 (1981). In addition, the DC conversion device 3 is disclosed in Japanese Unexamined Patent Publication JP-A 5-137326 (1993).
In order to drive the discharge tubes 5, the conventional liquid crystal display apparatus 1 has to give power to the discharge tubes 5 from the AC commercial power supply 2 via the first DC power generating circuit 10, the first alternating power generating circuit 11, the first transforming circuit 12, the second DC power generating circuit 13, the second alternating power generating circuit 14, and the second transforming circuit 15. In this case, power loss occurs in each of these circuits 10 to 15.
The conventional liquid crystal display apparatus 1 mentioned above converts commercial AC power into DC power with the DC conversion device 3, further converts the converted DC power into AC power of a high frequency and a high voltage with the inverter device 4, and gives the converted AC power to the discharge tubes 5.
In order to realize an increase in size and an increase in luminance of a display screen, in the liquid crystal display device 1, the discharge tubes 5 tend to be longer and increase in number. In this case, a ratio of power consumption of the discharge tubes 5 with respect to power consumption of the entire liquid crystal display apparatus increases. Since power loss in the DC conversion device 3 and the inverter device 4 increases in accordance with the increase in power consumption of the discharge tubes 5, there is a strong demand for improvement of the power loss in the power conversion.
Conventionally, improvement of the power loss has been pursued in the DC conversion device 3 and the inverter device 4, separately. However, significant reduction of the power loss has not been realized. In addition, such a problem is also present in a drive system that has a DC drive device and an AC drive device and is given AC power from a power source.